A volume rendering (VR) technique is known. In the VR technique, a medical image taken by a diagnostic imaging apparatus is reconstructed into volume image data, and then the resultant data is displayed on a monitor as a 2D image. To provide the volume image with a realistic sense of depth, it is also considered to display such an image in three dimensions. Three-dimensional display of medical images is expected to be applied in a variety of situations such as a preoperative conference, an operative planning simulation, and intraoperative navigation.
It is known that a 3D image is given in a stereoscopic view by typically using glasses for stereopsis, but recently, glasses-free 3D monitors have been developed that provide stereoscopic views without special glasses. If the glasses-free 3D monitors are applied in a medical field, for example, stereoscopic images can be utilized without bothersome glasses also in operation.
Also, in operation, since multiple persons may stereoscopically view a medical image simultaneously from different directions through a glasses-free 3D monitor, technology has been developed that enables stereopsis even if a glasses-free 3D monitor is viewed from every angle.
If a single object is stereoscopically viewed on a glasses-free 3D monitor, two or more multi-parallax images are displayed with different directivities. Thereby, the object can be stereoscopically viewed from multiple directions as well as from the front.
In medical practice, images of a plurality of objects may be displayed to make a comparative review of specific sites of the objects. In order to make a proper comparative review when a plurality of objects is stereoscopically viewed on a single screen, display of such objects has been considered in many ways. For example, there is a method for creating parallax images based on one focus in one virtual space including a plurality of objects.
However, if parallax images are created based on one focus in a virtual space including a plurality of objects, for the stereoscopic objects, a side facing a viewer from the focus and a side opposite thereto (inner sides of the objects) are viewed. Thus, each object is not displayed at a same side and a same angle, so that it is challenging for the viewer to make a comparative review.